Composite materials

ABSTRACT

A composite material is described which is characterized by a substrate based on glass fibers, mineral fibers or derived timber products and by a nanocomposite which is in functional contact with said substrate and is obtainable by surface modification of 
     a) colloidal inorganic particles with 
     b) one or more silanes of the general formula (I) 
     
       
         R x —Si—A 4-x   (I)  
       
     
     where the radicals A are identical or different and are hydroxyl groups or groups which can be removed hydrolytically, except methoxy, the radicals R are identical or different and are groups which cannot be removed hydrolytically and x is 0, 1, 2 or 3, where x≧1 in at least 50 mol % of the silanes; 
     under the conditions of the sol-gel process with a below-stoichiometric amount of water, based on the hydrolysable groups which are present, with formation of a nanocomposite sol, and further hydrolysis and condensation of the nanocomposite sol, if desired, before it is brought into contact with the substrate, followed by curing.

The invention relates to composite materials characterized by asubstrate based on glass fibers, mineral fibers or derived timberproducts and by a nanocomposite which is in functional contact with saidsubstrate and is obtainable by surface modification of

a) colloidal inorganic particles with

b) one or more silanes of the general formula (I)

R_(x)—Si—A_(4-x)  (I)

where the radicals A are identical or different and are hydroxyl groupsor groups which can be removed hydrolytically, except methoxy, theradicals R are identical or different and are groups which cannot beremoved hydrolytically and x is 0, 1, 2 or 3, where x≧1 in at least 50mol % of the silanes;

under the conditions of the sol-gel process with a sub-stoichiometricamount of water, based on the hydrolysable groups which are present,with formation of a nanocomposite sol, and further hydrolysis andcondensation of the nanocomposite sol, if desired, before it is broughtinto contact with the substrate, followed by curing.

The substrate may be of very different physical forms, and thenanocomposite may also be present in different forms of distribution.For example, the nanocomposite may cover the substrate partially orentirely in the form of a continuous covering or coating or it may bepresent between a plurality of substrates in lamellar form. Specificexamples of composite materials of this type are fibers, twines, yarns,and semifinished products such as wovens, knits, braids and non-wovensprovided with a thermally stable impregnation.

Alternatively the nanocomposite may form discontinuous or evenpoint-shaped sites of contact between a plurality of substrates and may,for example, bind a particulate, flocculant or fibrous substrate in amatrix-like manner. Specific examples of composite materials of thelatter type are insulating materials based on glass or mineral fibersand materials made of wood such as wood fiber slabs, particle boards,wood core plywood, plywood and wood-wool building slabs. For specialpurposes mixtures of glass fibers and timber materials may also beemployed, e.g., for chip boards having flame-retardant properties.

Examples of suitable substrates are glass fibers, natural or man-mademineral fibers such as asbestos, mineral wool, slag wool, and fibers ofceramic materials including those of oxide ceramic; materials derivedfrom timber in the form of cellulose, wood wool, wood flour, wood chips,paper, cardboard, wooden plates, wood borders and wood laminates.

The term fibrous substrates is taken to mean either individual fibers,including hollow fibers and whiskers, or corresponding fiber bundles,threads, ropes, twines and yarns, or semifinished products such aswovens, knits, braids, textiles, non-wovens, felts, webs, sheets andmats. Concrete examples of these are glass wool, glass fiber mats andmineral wool, e.g., slag wool, cinder wool, rock wool or basalt fibers.

The nanocomposite employed according to the invention is prepared bysurface modification of colloidal inorganic particles (a) with one ormore silanes (b), if desired in the presence of other additives (c)under the conditions of the sol-gel process.

Details of the sol-gel process are described in C. J. Brinker, G. W.Scherer: “Sol-Gel Science—The Physics and Chemistry ofSol-Gel-Processing”, Academic Press, Boston, San Diego, New York, Sydney(1990) and in DE 1941191, DE 3719339, DE 4020316 and DE 4217432.

Here, specific examples of the silanes (b) which can be employedaccording to the invention and of their radicals A which arehydrolytically removable and their radicals R which are nothydrolytically removable are given.

Preferred examples of groups A which are removable hydrolytically arehydrogen, halogen (F, Cl, Br and I, in particular Cl and Br), alkoxy (inparticular C₂₋₄-alkoxy, such as ethoxy, n-propoxy, isopropoxy andbutoxy), aryloxy (in particular C₆₋₁₀-aryloxy, such as phenoxy),alkaryloxy (e.g. benzyloxy), acyloxy (in particular C₁₋₄-acyloxy, suchas acetoxy and propionyloxy) and alkylcarbonyl (e.g. acetyl). Radicals Awhich are likewise suitable are amino groups (e.g. mono- or dialkyl-,-aryl- and -aralkylamino groups having the abovementioned alkyl, aryland aralkyl radicals), amide groups (e.g. benzamido) and aldoxime orketoxime groups. Two or three radicals A may also together form a moietywhich complexes the Si atom, as for example in Si-polyol complexesderived from glycol, glycerol or pyrocatechol. Particularly preferredradicals A are C₂₋₄-alkoxy groups, in particular ethoxy. Methoxy groupsare less suitable for the purposes of the invention, since they have anexcessively high reactivity (short processing time of the nanocompositesol) and can give nanocomposites and/or composite materials withinsufficient flexibility.

The abovementioned hydrolysable groups A may, if desired, carry one ormore usual substituents, for example halogen atoms or alkoxy groups.

The radicals R which are not hydrolytically removable are preferablyselected from alkyl (in particular C₁₋₄-alkyl, such as methyl, ethyl,propyl and butyl), alkenyl (in particular C₂₋₄-alkenyl, such as vinyl,1-propenyl, 2-propenyl and butenyl), alkynyl (in particularC₂₋₄-alkynyl, such as acetylenyl and propargyl), aryl (in particularC₆₋₁₀-aryl, such as phenyl and naphthyl) and the corresponding alkaryland arylalkyl groups. These groups may also, if desired, have one ormore usual substituents, for example halogen, alkoxy, hydroxy, amino orepoxide groups.

The abovementioned alkyl, alkenyl and alkynyl groups include thecorresponding cyclic radicals, such as cyclopropyl, cyclopentyl andcyclohexyl.

Particularly preferred radicals R are substituted or unsubstitutedC₁₋₄-alkyl groups, in particular methyl and ethyl, and substituted orunsubstituted C₆₋₁₀-aryl groups, in particular phenyl.

It is also preferable that x in the above formula (I) is 0, 1 or 2,particularly preferably 0 or 1. It is also preferable if x=1 in at least60 mol %, in particular at least 70 mol %, of the silanes of the formula(I). In particular cases, it may be even more favourable if x=1 in morethan 80 mol %, or even more than 90 mol % (e.g. 100 mol %), of thesilanes of the formula (I).

The composite materials according to the invention may be prepared, forexample, from pure methyltriethoxysilane (MTEOS) or from mixtures ofMTEOS and tetraethoxysilane (TEOS), as component (b).

Concrete examples of silanes of the general formula (I) are compounds ofthe following formulae:

Si(OC₂H₅)₄, Si(O-n-or iso-C₃H₇)₄, Si(OC₄H₉)₄, SiCl₄,

Si(OOCCH₃)₄, CH₃—SiCl₃, CH₃—Si(OC₂H₅)₃, C₂H₅—SiCl₃,

C₂H₅—Si(OC₂H₅)₃, C₃H₇—Si(OC₂H₅)₃, C₆H₅—Si—(OC₂H₅)₃,

C₆H₅—Si(OC₂H₅)₃, (C₂H₅O)₃—Si—C₃H₆—Cl, (CH₃)₂SiCl₂,

(CH₃)₂Si(OC₂H₅)₂, (CH₃)₂Si(OH)₂, (C₆H₅)₂SiCl₂,

(C₆H₅)₂Si(OC₂H₅)₂, (C₆H₅)₂Si(OC₂H₅)₂,

(iso-C₃H₇)₃SiOH, CH₂═CH—Si(OOCCH₃)₃, CH₂═CH—SiCl₃,

CH₂═CH—Si(OC₂H₅)₃, HSiCl₃,

CH₂═CH—Si(OC₂H₄OCH₃)₃, CH₂═CH—CH₂—Si(OC₂H₅)₃,

CH₂═CH—CH₂—Si(OOCCH₃)₃, CH₂═C(CH₃)COO—C₃H₇—Si—(OC₂H₅)₃,

CH₂═C(CH₃)—COO—C₃H₇—Si(OC₂H₅)₃, n—C₆H₁₃—CH₂—CH₂—Si(OC₂H₅)₃,

n-C₈H₁₇—CH₂—CH₂—Si(OC₂H₅)₃,

These silanes can be prepared by known methods; cf. W. Noll, “Chemie undTechnologie der Silicone” [Chemistry and Technology of the Silicones],Verlag Chemie GmbH, Weinheim/Bergstraβe, Germany (1968).

Based on the abovementioned components (a), (b) and (c), the proportionof component (b) is usually from 20 to 95% by weight, preferably from 40to 90% by weight, and particularly preferably from 70 to 90% by weight,expressed as polysiloxane of the formula: R_(x)SiO_((2−0.5x)) which isformed in the condensation.

The silanes of the general formula (I) used according to the inventionmay be employed wholly or partially in the form of precondensates, i.e.compounds produced by partial hydrolysis of the silanes of the formula(I), either alone or in a mixture with other hydrolysable compounds.Such oligomers, preferably soluble in the reaction medium, may bestraight-chain or cyclic low-molecular-weight partial condensates(polyorganosiloxanes) having a degree of condensation of e.g. from about2 to 100, in particular from about 2 to 6.

The amount of water employed for hydrolysis and condensation of thesilanes of the formula (I) is preferably from 0.1 to 0.9 mol, andparticularly preferably from 0.25 to 0.75 mol, of water per mole of thehydrolysable groups which are present. Particularly good results areoften achieved with from 0.35 to 0.45 mol of water per mole of thehydrolysable groups which are present.

Specific examples of colloidal inorganic particles (a) are sols andpowders dispersible at the nano level (particle size preferably up to300 nm, in particular up to 100 nm and particularly preferably up to 50nm) of SiO₂, TiO₂, ZrO₂, Al₂O₃, Y₂O₃, CeO₂, SnO₂, ZnO, iron oxides orcarbon (carbon black and graphite), in particular of SiO₂.

The proportion of component (a), based on the components (a), (b) and(c), is usually from 5 to 60% by weight, preferably from 10 to 40% byweight, and particularly preferably from 10 to 20% by weight.

For preparing the nanocomposite, other additives in amounts of up to 20%by weight, preferably up to 10% by weight, and in particular up to 5% byweight, may be employed as optional components (c); examples are curingcatalysts, such as metal salts and metal alkoxides (e.g. aluminiumalkoxides, titanium alkoxides or zirconium alkoxides), organic binders,such as polyvinyl alcohol, polyvinyl acetate, starch, polyethyleneglycol and gum arabic, pigments, dyes, flame retardants, compounds ofglass-forming elements (e.g. boric acid, boric acid esters, sodiummethoxide, potassium acetate, aluminium sec-butoxide, etc.),anti-corrosion agents and coating aids. According to the invention, theuse of binders is less preferred.

The hydrolysis and condensation is carried out under sol-gel conditionsin the presence of acid condensation catalysts (e.g. hydrochloric acid)at a pH of preferably from 1 to 2, until a viscous sol is produced.

It is preferable if no additional solvent is used besides the solventproduced in the hydrolysis of the alkoxy groups. If desired, however,alcoholic solvents, such as ethanol, or other polar, protic or aproticsolvents, such as tetrahydrofuran, dioxane, dimethylformamide or butylglycol, for example, may be employed.

In order to achieve a favourable sol particle morphology and solviscosity, the resultant nanocomposite sol is preferably subjected to aspecial post-reaction step in which the reaction mixture is heated totemperatures of from 40 to 120° C. over a period of from a number ofhours to a number of days. Special preference is given to storage forone day at room temperature or heating for a number of hours at from 60to 80° C. This gives a nanocomposite sol with a viscosity of preferablyfrom 5 to 500 mPas, particularly preferably from 10 to 50 mPas. Theviscosity of the sol can also, of course, be adjusted to suitable valuesfor the specific application by adding solvents or removingside-products of the reaction (e.g. alcohols). The post-reaction stepmay preferably also be coupled with a reduction of the solvent content.

The proportion by weight of the nanocomposite in the composite materialis preferably from 0.1 to 80% by weight, in particular from 1 to 40% byweight, and particularly preferably from 1 to 20% by weight.

The substrate and the nanocomposite or nanocomposite sol are combinedafter at least initial hydrolysis of component (b) and in any casebefore final curing. Before it is brought into contact with thesubstrate, the nanocomposite sol is preferably activated by feeding in afurther amount of water.

The contact can be brought about by any means known to the personskilled in the art and deemed to be useful for the particular case, e.g.by simple mixing of substrate and nanocomposite sol, dipping, sprayingor showering, knife- or spin-coating, pouring, spreading, brushing,etc., into the or with the nanocomposite sol. In order to improve theadhesion between substrate and nanocomposite, it may be advantageous inmany cases to subject the substrate, before contact with thenanocomposite or its precursor, to a conventional surface pretreatment,e.g. corona discharge, degreasing, treatment with primers, such asaminosilanes, epoxy silanes, sizes made from starch or silicones,complexing agents, surfactants etc.

Before final curing, a drying step at room temperature or slightlyelevated temperature (e.g. up to about 50° C.) may be undertaken.

The actual curing or a precuring can be carried out at room temperature,but preferably by heat treatment at temperatures above 50° C.,preferably above 100° C. and particularly preferably at 150° C. orabove. The maximum curing temperature depends, inter alia, on themelting point and/or the heat resistance of the substrate, but isgenerally from 250 to 300° C. With mineral substrates, however,significantly higher curing temperatures are also possible, e.g. from400 to 500° C. and above. Curing times are generally in the range fromminutes to hours, e.g. from 2 to 30 minutes.

Besides conventional curing by heat (e.g. in a circulating air oven)other curing methods may be used, for example curing with IR beams orlaser beams. If desired, the composite prepared may also be subjected toa shaping process before curing.

The invention also relates to the use of the abovementionednanocomposite for the coating and/or consolidation of the abovementionedsubstrates. The term “consolidation” is intended here to include anymeasure which is suitable for providing the substrate in consolidatedand/or compacted form, and thus includes, for example, impregnation ofthe substrate with nanocomposite, embedding of the substrate into amatrix of nanocomposite or cementation or binding of substrates orpieces of substrate with nanocomposite. The term “coating” is taken tomean in particular a partial or complete encapsulation of a substratewith a nanocomposite in order to give this substrate, or pieces thereof,particular properties, for example oxidation resistance, flameretardancy, hydrophobic or oleophobic character, hardness,impermeability, or electrical or thermal insulation.

The following examples further illustrate the present invention. In thefollowing examples, the silica sol employed is an aqueous silica solfrom BAYER (“Levasil 300/30”) with a solids content of 30% by weight anda particle size of from 7 to 10 nm. The following abbreviations arefurthermore used in the examples:

MTEOS=Methyltriethoxysilane

TEOS=Tetraethoxysilane

PTEOS=Phenyltriethoxysilane

EXAMPLE 1

A mixture of 65 mole % of MTEOS, 15 mole % of PTEOS and 20 mole % ofTEOS (or, alternatively, of 80 mole % of MTEOS and 20 mole % of TEOS) isvigorously stirred with silica sol and hydrochloric acid as catalyst inorder to prepare a nanocomoposite sol by hydrolysis and condensation ofthe silanes. The amount of water introduced by means of the silica solis such that 0.8 moles of water are present per mole of hydrolysablegroup. About 5 minutes after the preparation of the sol the above silanemixture is added thereto so that the total water content of theresulting mixture is 0.4 moles of water per mole of alkoxy groups. Thesilica sol accounts for about 14 wt. % of the total solids content.

Following a post-reaction phase of about 12 hours at room temperature,water is added to the above mixture in an amount which results in atotal water content of the sol of 0.5 moles of water per mole of alkoxygroups. After about 5 minutes the mixture is ready for use.

The ready-for-use mixture is sprayed onto dampened glass wool through anatomizing ring and cured for about 5 to 10 minutes in a circulating airoven at about 200° C. Thereby an elastic insulating material showinghighly improved flame properties in comparison to glass wool bonded withphenolic resin is obtained.

EXAMPLE 2

68.7 ml of MTEOS (corresponding to 80 mole %) and 19.2 ml of TEOS(corresponding to 20 mole %) are mixed and half of said mixture isvigorously stirred with 11.7 ml of silica sol (corresponding to aproportion of 14.3% by weight of silica sol) and 0.386 ml ofconcentrated hydrochloric acid. Five minutes later the second half ofthe silane mixture is added to the run, whereafter stirring is continuedfor a further 5 minutes. Subsequently the resulting sol is subjected toa post-reaction step (allowing it to stand at room temperature for 2hours). Thereby a storage-stable precondensate having a SiO₂ solidscontent of about 300 g/l and 0.4 moles of water per mole of hydrolysablegroup is obtained. By concentration on a rotary evaporator the solidscontent is adjusted to 60 wt. %.

Prior to the application of the binder, 3.0 ml of titanium isopropylateand about 2.5 ml of water are added thereto in order to reach a watercontent of 0.5 moles of water per mole of hydrolysable group. Themixture thus prepared is mixed with wood chips in an amount whichresults in 15% of the composition consisting of SiO₂. Subsequently thecomposition is bonded in a hot press at 180° C. for 10 minutes to form ashaped body. Thereby a shaped body resembling a common glaced insulatingpress board is obtained, which body is, however, prepared withoutorganic binder. The flame properties of a corresponding plate aresignificantly improved in comparison to those of a conventional glacedinsulating press board.

EXAMPLE 3

1. Preparation of the sol

172 ml of MTEOS are mixed with 48 ml of TEOS. 29 ml of silica sol and 2ml of sulfuric acid (35%) are added thereto with vigorous stirring. Fiveminutes thereafter an opaque sol has formed which is allowed topost-react for 4 hours at room temperature. Following the addition of afurther 3 ml of water with stirring the mixture is ready for use afterabout 5 minutes.

2. Application of the sol

2.1

100 g of wood chips are mixed with 60 ml of sol and molded under apressure of 7.1 mPa in a press mold having a diameter of 12 cm for 10minutes. Subsequently the molding is pressed in a heatable press (upperand lower mold heated) at a pressure of 2.6 mPa and a temperature of100° C. for about 3 hours. Thereby a mechanically stable shaped bodyhaving a wood chips content of 82 wt. % is obtained.

2.2

300 g of rock wool granules are mixed with 10 ml of the above sol andare pressed at a pressure of 4.4 mPa in a press mold having a diameterof 12 cm for 5 minutes. Subsequently the molding is exposed to atemperature of 80° C. for 8 hours in a circulating air dryer. Thereby amechanically stable shaped body having a content of rock wool granulesof 1 wt. % is obtained.

We claim:
 1. A method of manufacturing a composite material comprising asubstrate selected from the group consisting of glass fibers, mineralfibers, and timber derived products, and a nanocomposite in functionalcontact with the substrate, the method comprising: (1) surface modifyingcolloidal inorganic particles with one or more silanes of the generalformula R_(x)—Si—A_(4-x) where each A is the same or different and isselected from hydroxyl and groups that are hydrolytically removable butare not methoxy, each R is the same or different and is selected fromgroups that are not hydrolytically removable, and x is 0, 1, 2, or 3,where x≧1 in at least 50 mol % of the silanes; under sol-gel processconditions with a quantity of water that is sub-stoichiometric based onthe quantity of hydrolytically removable groups present on the silanes,thereby preparing a nanocomposite sol; (2) optionally furtherhydrolyzing and condensing the nanocomposite sol; (3) optionallyactivating the nanocomposite sol with a further quantity of water; (4)contacting the substrate with the nanocomposite sol; and (5) curing thecontacted substrate, thereby forming the composite material.
 2. Themethod of claim 1 where the step of preparing the nanocomposite sol iscarried out in the presence of an acid condensation catalyst at a pH offrom 1 to
 2. 3. The method of claim 1 where the step of furtherhydrolyzing and condensing the nanocomposite sol takes place at atemperature between room temperature and 120° C.
 4. The method of claim1 where the colloidal inorganic particles are selected from the groupconsisting of sols and dispersible nanoscale powders of TiO₂, ZrO₂,Al₂O₃, Y₂O₃, CeO₂, SnO₂, ZnO, iron oxides, and carbon.
 5. The method ofclaim 1 where the colloidal inorganic particles comprise from 5% to 60%by weight of the nanocomposite.
 6. The method of claim 1 where thesilanes, when expressed as polysiloxane of the formulaR_(x)SiO_((2−0.5x)), comprise from 20% to 95% by weight of thecomposite.
 7. The method of claim 1 where additives are added duringpreparation of the nanocomposite sol.
 8. The method of claim 7 where theadditives are selected from the group consisting of curing catalysts,organic binders, pigments, dyes, flame retardants, compounds ofglass-forming elements, anti-corrosion agents, and coating aids.
 9. Themethod of claim 7 where the additives comprise not more than 20% byweight of the nanocomposite.
 10. The method of claim 1 where each A isselected from C₂₋₄ alkoxy.
 11. The method of claim 1 where each R isselected from optionally substituted C₁₋₄ alkyl and optionallysubstituted C₆₋₁₀ aryl.
 12. The method of claim 1 where the quantity ofwater used in the step of preparing the nanocomposite sol is from 0.1 to0.9 mol of water per mol of hydrolytically removable groups in thesilanes.
 13. The method of claim 1 where the nanocomposite comprisesfrom 0.1 to 80% by weight of the composite material.
 14. The method ofclaim 1 where the step of curing the contacted substrate comprisesthermal curing.
 15. The method of claim 1 where the substrate is coatedwith the nanocomposite.
 16. The method of claim 1 where the substrate isconsolidated with the nanocomposite.
 17. The method of claim 1 where thesubstrate is a fabric and is impregnated with the nanocomposite.
 18. Themethod of claim 1 which further comprises forming a laminate bysandwiching the composite material between laminate layers.
 19. Acomposite material manufactured by the method of claim
 1. 20. Acomposite material manufactured by the method of claim 1.